We present a novel information or key encryption and transmission technique based on phase-shifting digital holography for a security system. Phase-shifting digital holography is used for recording phase and amplitude information on CCD device. 4-step phase-shifting is implemented by moving the PZT mirror with equidistant phase steps of π /2. The information and the key are converted to random phase patterns. Digital hologram in this method is Fourier transform hologram and quantized with 256 gray-level. The basic idea is that we reuse a 256 gray-level digital hologram to encrypt the information or the key with 4-step phase-shifting digital holography. The encrypted binary data/image in the form of digital hologram can be transmitted through communication network, and is reconstructed and decrypted digitally. The simulation shows that the proposed method gives good results for a successive encryption/transmission.

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We propose a new optical one-time password(OTP) authentication method by using digital holography, which enhances security strength in the cryptosystem compared to the conventional electronic OTP method. In this paper, a challengeresponse optical OTP authentication based on two-factor authentication is presented by 2-step quadrature phase-shifting digital holography using orthogonal polarization, and two-way authentication is also performed using the challengeresponse handshake in both directions. The ID(identification), PW(password) and OTP information are encrypted with a shared key by applying phase-shifting digital holography, and these encrypted information are verified each other by the shared key. Because the encrypted digital holograms which are transmitted to the other party are expressed as random distribution, it guards against a replay attack and results in higher security level. Optically, encrypted digital hologram in our method is Fourier transform hologram and is recorded on CCD with 256 gray-level quantized intensities. The proposed method has an advantage that it does not need a time-synchronized OTP and can be applied to various security services. Computer experiments show that the proposed method is suitable for high secure OTP authentication.

We propose a digital holographic interference analysis method based on 2-step phase-shifting technique for measuring optical surface. The technique using 2-step phase-shifting digital interferometry is more efficient than multi-step phaseshifting techniques because 2-step method has an advantage of the reduced number of interferograms. In this measurement system, 2-step phase-shifting digital interferograms are acquired by moving the reference flat mirror surface which is attached to PZT with phase step of 0 or π/2 in the reference beam path and are recorded on CCD device. The optical interferometry is designed on the basis of polarization characteristics of polarizing beam splitter. Therefore the noise from outside turbulence can be decreased. The proposed 2-step algorithm uses the relative phase difference of the neighbor pixels. Experiment has been carried out on the optical mirror. The measurement of the optical mirror surface topography shows that the result using 2-step algorithm is similar to that of other multi-step algorithms. Thus, the proposed method is expected to be used in nondestructive testing of optical components.

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